1. Technical Field
This invention relates generally to the field of vascular dilatation, such as angioplasty, and more particularly to new and improved balloon catheters for use in such procedures, and to method for making such balloon catheters.
2. Background Art
Cardiac catheterization procedures are well known for diagnosis and therapy of lesions in the cardiovascular system, such as vascular blockage. One such procedure is angioplasty for eliminating or reducing the vascular plaque blockage or constriction in blood vessels associated with providing blood supply to the heart. In such angioplasty procedures, an expandable balloon is introduced into the patient's arterial system and advanced until it is positioned in the region of the blockage or constriction. Once so positioned, the balloon is expanded by inflating it with a liquid. In successful procedures, the expandable balloon presses outwardly against the walls of the blocked artery and expands the artery to a degree to which the artery is either partially or totally re-opened to blood flow.
Typical angioplasty procedures, and components used in practicing the procedures, are now described.
Prior to initiating the angioplasty procedure, a guiding catheter is advanced, typically via the femoral artery into the aorta, with its distal tip is located at or near the ostium, i.e., the location at which the coronary arteries begin to branch from the aorta. Once placed, the guiding catheter acts as a conduit to access the coronary arteries with a balloon guidewire and a balloon catheter.
The guiding catheter is a portion of plastic tubing having a length of about 95 centimeters, and interior diameter of about 0.08 inches, and an outside diameter of about 2.5 millimeters.
The physician performing the procedure threads a balloon catheter onto a balloon guidewire. This operation takes place external to the patient.
The balloon guidewire is a piece of stainless steel and platinum wire, approximately 175 centimeters in length, and about 0.010-0.018 inches in diameter. A soft distal tip of the guidewire can be shaped to form a "J" configuration. This "J" shape facilitates the physician steering the wire by twisting the proximal extremity of the wire while advancing or retracting the wire.
The balloon catheter is an elongated flexible plastic member defining two longitudinal passages and having a balloon located near its distal end. One longitudinal opening defines a balloon guidewire lumen, which forms a sleeve through which the balloon guidewire can be threaded. Another longitudinal passage, an inflation lumen, defines a conduit communicating with the interior of the balloon and through which inflation fluid can be injected to inflate the balloon.
Among the types of balloon catheters is one in which the two longitudinal passages are generally side by side and parallel. This is often referred to as a "dual lumen" balloon catheter. In another type of balloon catheter, the two longitudinal passages are coaxial. This type of balloon catheter is often called a "coaxial lumen catheter". In a coaxial lumen catheter, the balloon guidewire is threaded down the inner passage, which forms the guidewire lumen, and the inflation fluid is injected into the balloon via the outer passage, which forms the inflation lumen.
The physician threads the balloon guidewire through the guidewire lumen in the balloon catheter, leaving a portion of the balloon guidewire extending from the distal end of the balloon catheter and also a portion extending from the proximal end of the balloon catheter.
This assembly, including the balloon guidewire and balloon catheter, is then inserted into the proximal end of the guiding catheter, distal end first. The assembly is inserted until the balloon, which is attached near the distal end of the balloon catheter, is near the distal end of the guiding catheter. At this point, the physician, while maintaining the balloon catheter stationary, pushes on the balloon guidewire to advance it outwardly from the distal end of the guiding catheter.
The balloon guidewire can be steered by appropriate twisting movement by the physician.
The physician steers the balloon guidewire into the chosen one of the coronary arteries, and advances it until its distal end reaches a location of constriction which the physician desires to re-open. Carefully, the physician eases the balloon guidewire through the region of restriction until a portion of the balloon guidewire is on the opposite side of the constriction, relative to the guiding catheter.
With the balloon guidewire held stationary, the physician then advances the balloon catheter. The distal end of the balloon catheter, as it is advanced, will, of course, follow the balloon guidewire which is already in place.
The physician continues to advance the balloon until it is located in the region of the constriction of the artery. With the balloon and its associated catheter held stationary, inflation fluid is injected into the inflation lumen which communicates with the interior of the balloon, causing the balloon to inflate. Inflation of the balloon expands the walls of the artery in the region of constriction and, in successful procedures, re-opens the artery to sufficient blood flow.
Both dual lumen and coaxial lumen catheters have particular advantages and disadvantages.
One advantage of a dual lumen catheter is that it can be relatively stiff, both laterally and axially. This is due to the fact that the two lumens are integrally formed as a portion of the catheter shaft, and are unable to move relative to one another. The rigidity enhances the ability of the physician to push the balloon catheter when desired for advancement of the balloon. Additionally, the dual lumen construction permits direct access to the guidewire lumen through a slit in the side of the catheter, facilitating the guidewire exiting the guidewire lumen on the side, rather than from the end, of the catheter. Such side access to the guidewire lumen is not possible in coaxial lumen catheters, because such access would necessarily require piercing of the outer coaxial inflation lumen in a coaxial design. A further advantage of dual lumen catheters is that there is greater design flexibility in sizing the cross-sectional area of the inflation lumen to optimize inflation fluid flow. The cylindrical inflation lumen made possible in a dual lumen construction has a greater ratio of cross-sectional area to cross-sectional perimeter than does the annular cross-sectioned inflation lumen in the coaxial construction.
Despite all the advantages inherent in the dual lumen construction, the rigidity of the dual lumen design is a disadvantage at the distal end of the catheter. The more rigid dual lumen design is not as compliant as is the coaxial design and therefore is not as facile in tracking tortuous turns in blood vessels through which the catheter is advanced.
Catheters of coaxial lumen design are more compliant and flexible than dual lumen design catheters. This is because the walls of the coaxial lumens can move relative to one another when bending forces are applied to the catheter shaft. This relative movement is not possible in catheters of the dual lumen construction.
It is a general object of the present invention to provide a balloon catheter shaft exhibiting the benefits of both the dual lumen and coaxial constructions, without the disadvantages of either design.